If you want to see just the lines with content, such as in a config file, use this one-liner:
grep -viE '^\s*((#|;).*)?$' smb.conf
How it works
grep -v means invert the selection, i.e., everything that does not match this search.
-iE case Insensitive, and treat this as a regular Expression. Technically there are no letters being searched, so the i is irrelevant, but I always use it in my searches anyway.
^ start of line
\s* white space, any amount from zero onward. This is a greedy search, so it will match all the white space (spaces, tabs, etc.)
(#|;) either a pound or a semicolon, which usually denote comments in config files (in my case, smb.conf)
((#|;).*) the above sentence, followed by any character (the period), and any amount of those “any characters.”
((#|;).*)? the whole thing in parentheses shown here, optionally.
$ end of line
So any line that starts with any amount of white space, followed by (a comment symbol, followed by anything else) optionally, and the end of the line.
So show everything but the above sentence, and tada, just the important stuff.